Coherent spin pumping in a strongly coupled magnon-magnon hybrid system
Yi Li, Wei Cao, Vivek P. Amin, Zhizhi Zhang, Jonathan Gibbons, Joseph Sklenar, John Pearson, Paul M. Haney, Mark D. Stiles, William E. Bailey, Valentine Novosad, Axel Hoffmann, Wei Zhang
We have experimentally identified coherent spin pumping acting as a dampinglike coupling in the magnon-magnon hybrid modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband ferromagnetic resonance, an ``avoided crossing" is observed well above the linewidths between the uniform mode of Py and the spin wave mode of YIG, which is due to the fieldlike interfacial exchange coupling. We also identify additional linewidth suppression and enhancement for the higher- and lower-frequency hybrid modes, respectively. The results can be fully reproduced by an analytical model incorporating mutual spin pumping from the coherent dynamics of Py and YIG. The model predicts inverse proportionality of both fieldlike and dampinglike torques to the square root of the Py thickness, which quantitatively agrees with experiments.